Harvard Psychological Studies, Volume 1 eBook

than the first, and unless this is due to the partial
exhaustion of the nervous system it is hard to find
an explanation of the fact. Fatigue of the muscles
concerned seems out of the question because the reactions
occur at the rate of only one per minute, and during
the rest interval any healthy and well-nourished muscle
would so far recover from the effect of contraction
that it would be able to continue the rhythmic action
for long periods.

To the inquiry, Does fatigue in the experiments mean
tiring by the exhaustion of nerve energy, or is the
lengthening in reaction time which would naturally
be attributed to tiring due to the fact that experience
has shown quick reaction to be unnecessary? we shall
have to reply that there is evidence in favor of both
as factors. There can be little doubt that in
case of the strong stimuli there is genuine fatigue
which makes quick reaction impossible; but at the same
time it is certain that the 40 to 50 per cent. increase
of the second half of sets in series 1 over the first
half can not be due to fatigue, for the strain is
here evidently much less than for series 3. Rather,
it would seem that habituation instead of exhaustion
is the all-important cause of the difference in series
1 and 2. It becomes clear from these considerations
that the repetition of a stimulus can never mean the
repetition of an effect.

VII. TACTUAL REACTION TIME.

In the following work on the reactions to tactual
stimulation the subject was placed in a large reaction
box with a thread attached to one of its legs and
passing to a reaction key, as in the experiments already
described. The box in which the subject was confined
was surrounded by movable cloth curtains to prevent
the animal’s escape and at the same time permit
the experimenter to work without being seen by the
frog.

Tactual stimulation was given by means of a hand key[15]
similar to that used for electrical stimulation which
is represented in Fig. 6. The touch key ended
in a hard-rubber knob which could be brought in contact
with the skin of the subject. This key was fixed
to a handle of sufficient length to enable the operator
to reach the animal wherever it chanced to be sitting
in the reaction box. Stimulation was given by
allowing the rubber point of the touch key to come
in contact with the skin in the middle region of the
subject’s back. As soon as the point touched
the animal the chronoscope circuit was broken by the
raising of the upper arm of the key.

[15] This apparatus was essentially
the same as Scripture’s
device for the giving of tactual
stimulation.

As a precaution against reactions to visual stimuli,
which it might well be supposed would appear since
the subject could not in every case be prevented from
seeing the approaching apparatus, the frog was always
placed with its head away from the experimenter so
that the eyes could not readily be directed toward
the touch apparatus. Notwithstanding care in
this matter, a reaction occasionally appeared which
was evidently due to some disturbance preceding the
tactual stimulus which served as a warning or preparation
for the latter. All such responses were at once
marked as questionable visual reactions and were not
included in the series of touch reactions proper.